The purpose of this study is to determine the extent to which body fat, regional distribution of fat, and fitness influence growth hormone (GH) secretion in young, middle-aged, and older adults. These relationships will be examined during spontaneous, fasting and exercise conditions. Body composition will be determined using a 4 compartment model and GH section by frequent sampling. We will also investigate whether the decrease in GH secretion with aging is due to a decrease in GH pulse frequency, amplitude, or some combination of these facts. Will not study middle-aged subjects.